1. Field of the Invention
The present invention relates to a turn control apparatus for a vehicle, and more specifically, to an apparatus for controlling yawing of a vehicle.
2. Description of the Related Art
Yaw rate sensors for detecting yaw rates that indicate the degrees of yawing of objects go into actual use and are used in operation control for vehicles, for example. A vehicle turn behavior control apparatus that uses a yaw rate sensor is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 3-112755. In this control apparatus, the actual yaw rate of a vehicle is detected by means of the yaw rate sensor, and a target yaw rate is computed in accordance with the steering-wheel angle and vehicle velocity. Also, a brake fluid pressure for yaw rate compensation such that the actual yaw rate is approximated to the target yaw rate is computed for each of the inside and outside wheels in a turn. The fluid pressure is supplied to the wheel cylinder of each wheel so that the yaw rate obtained is conformable to the operating conditions of the vehicle.
It is advisable to start the vehicle turn control of this type immediately when it is requested as the vehicle turns yawing excessively or inadequately. Accordingly, the brake fluid pressure for turn control (yaw rate compensation) must be generated as soon as the turn control is requested.
In the case where a pump is used as a source of the brake fluid pressure for turn control, It is to be desired that the pump should be kept continually actuated to shorten a delay in response of the brake fluid pressure to the request for the turn control. In order to meet a demand that the energy consumption for the vehicle drive should be cut down, on the other hand, it is advisable to reduce energy consumed by the actuation of the pump. This may be attained by designing the pump so that it cannot be actuated when the vehicle is not subject to the turn control and can start operation when the turn control is requested. It is difficult, however, fully to raise the fluid pressure the moment the pump is actuated, so that actuating the pump in response to the turn control request is subject to a response delay.
In the apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 3-112755, a brake fluid pressure for turn control, generated by means of a pump, is previously stored in an accumulator, and is supplied to wheel brakes when turn control is started. According to this arrangement, the delay in response to the turn control request can be removed. The use of the accumulator, however, renders the apparatus more complicated in construction and requires a wider installation space. Thus, it is impractical to furnish a small vehicle, such as a passenger car, with the turn control apparatus with accumulator.